This invention relates to systems and methods for forming an object.
Mass customization is the application of mass production techniques to the production of parts that are different from each other and produced in rapid sequence. Mass-producing items that are generically similar to each other using production equipment that is rapidly modifiable or reprogrammable allows differences between there items.
One way to perform mass customization is to apply pressure forming to plastic materials. Current pressure forming technology uses convection, conduction and insulation to heat plastic for thermoforming. These methods are either ‘bulk’ heating with a homogeneous heating of the entire sheet, or are tailored for repeating the same process on one form; neither method is adaptable to custom heating control with different parts with mass production throughput. Current technology does not differentiate zones of different temperatures on the formed sheet in order to optimize the shape and thickness profile of the formed part, individually. Homogeneous heating allows the forming of material to draw (stretch) more on surfaces that are more parallel to the general direction of the forming draw, thus creating parts with widely varying thickness throughout. This result is often undesirable, as in the case of Orthodontic Aligners where ‘bite’ surfaces are thicker than other surfaces as a result. Current methods for controlling the heating profile are mechanically built-in and static, so they do not lend themselves to rapid process improvements, nor do they allow rapid re-programming for new shapes of thermoformed parts.
Thermoforming is a process of heating plastic sheet materials to their glass-transition temperature range, deforming them to a desired shape, then cooling them in order to set the new shape. A die, or solid form is used to define the 3D shape that the sheet will acquire as it transforms from a two-dimensional sheet when it is heated and forced to conform to the three-dimensional surface of the die. Transformation of the 2D sheet depends on its stretching around the die contours, thinning as it stretches. This stretching, in terms of where and how much, is dependent on localized stresses and localized flexural modulus in the plastic; this action is interdependent between areas of the forming sheet so that stress distribution and modulus distribution define the final stretching and thickness distribution. If stress and modulus distribution are controlled, then stretching distribution can be controlled. The major determinant of forming stress is final shape and is controlled by the form of the die, so control of the modulus through temperature control will yield control of the thickness. Such control must account for the die shape and is admittedly complex, but is within the computational power of current computers and programs.
Flexural modulus is highly dependent on temperature. Control over localized temperature variation will result in control of stretching and thickness. As the sheet material is forming over the die, hotter areas will stretch more than cooler areas when all of these areas are within the glass-transition temperature range. This temperature/modulus control of areas will enable management of stretching within the distributed pattern of stresses, resulting in the control of thickness throughout the formed part.